Test
Chapter 3 (True/False)
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Preguntas del test (30)
11) The practical significance of taking the logical view of a database is that is serves as reminder of the simple file concept of data storage.
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22) You can think of a table as a persistent representation of a logical relation.
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33) Because the relational model uses attribute values to establish relationships among tables, many data-base susers correctly assume that the term relation refers to such relationships.
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44) The order of the rows and columns is important to the DBMS.
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55) Numeric data are data on which you can perform meaningful arithmetic procedures.
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66) Character data can contain any character or symbol intended for mathematical manipulation.
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77) Each table in a relational database must have a primary key.
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88) The idea of determination is unique to the database environment.
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99) In a relational model, if A determines B, C, and D, you write A = B, C, D.
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1010) Only a single attribute, not multiple attributes, can define functional dependence.
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1111) If the attribute (B) is functionally dependent on a composite key (A) but not on any subset of that composite key, the attribute (B) is fully functionally dependent on (A).
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1212) A null is created when you press the Enter key or the Tab key to move to the next entry without making a prior entry of any kind.
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1313) There is never a good reason to use null values in a database.
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1414) Depending on the sophistication of the application development software, nulls can create problems when functions such as COUNT, AVERAGE, and SUM are used.
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1515) Tables within a database share common attributes that enable the tables to be linked together.
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1616) A foreign key must exist in both tables that have a relationship
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1717) RDBMSs enforce integrity rules automatically.
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1818) Referential and entity integrity are two names for the same thing.
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1919) The SELECT operator yields a vertical subset of a table.
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2020) Tables must have the same attribute characteristics (the columns and domains must be compatible) to be used in a UNION.
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2121) The DIFFERENCE operator subtracts one table from the other.
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2222) In a natural join, the column on which the join was made occurs twice in the new table.
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2323) A left outer join on tables CUSTOMER and AGENT yields all of the rows in the CUSTOMER table, including those that do not have a matching value in the AGENT table.
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2424) The DIVIDE operation uses one single-column table (e.g., column "a") as the divsor and one two-column table (e.g., columns "a" and "b") as the dividend.
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2525) A data dictionary contains metadata-data about data.
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2626) A data dictionary is sometimes described as :the database designer's database" because it records the design decisions about tables and their structures.
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2727) Current relational database software generally provides only a system catalog (and not a data dictionary).
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2828) The one-to-many (1:M) relationship is easily implemented in the relational mode by putting the foreign key of the "1" side in the table of the "many" side as a primary key.
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2929) As rare as 1:! relationships should be, certain conditions absolutely require their use.
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3030) DBMSs use indexes for many different purposes.
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Información
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- asdf Test sobre Chapter 3 (True/False), creado por . . el 31/08/2016.
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